The objective of this research is to study the ultrastructure of various species of malaria parasites in different developmental stages and interaction between the parasites and host cells by high voltage electron microscopy. In the current year we studied microgametogenesis of Haemoproteus columbae by high voltage and conventional electron microscopy. The features of microgametogenesis which have become clear by high voltage electron microscopy include the distribution and arrangement of axonemes in the microgametocyte and the budding process and structure of the microgametes. High voltage electron microscopy shows that prior to exflagellation the axonemes occupy a major portion of the cytoplasm, and are arranged in an orderly fashion. A short portion of the axoneme protrudes outward in the early state of microgamete budding, while the major portion remains within the cytoplasm. The microgamete is composed of a slender nucleus and an axoneme which run along the same axis and spiral one another. The nucleus is slightly bulbous at the anterior end and at the midportion of the microgamete. These findings have not been obtained with certainty by conventional electron microscopy. For the on-coming year, we will study nuclear division of malarial parasites by high voltage electron microscopy.